Drying gypsum wallboard



May 7, 1963 c. J. LOECHL DRYING GYPSUM WALLBOARD Original Filed Feb. 23, 1956 2 Sheets-Sheet 1 Q Y Irv/222101". Clo rerza afaeakl. j mm. W y librny May 7, 1963 C. J. LOECHL DRYING GYPSUM WALLBOARD Original Filed Feb. 23, 1956 2 Sheets-Sheet 2 United States Patent 3,088,218 DRYING GYPSUM WALLBOARD Clarence J. Loechl, Arlington Heights, 11]., assignor to The Celotex Corporation, Chicago, 11L, a corporation of Delaware Griginai application Feb. 23, 1956, Ser. No. 567,162, now hatent No. 2,909,850, dated Oct. 27, 1959. Divided and this application May 20, 1958, Ser. No. 736,553 4 Claims. (Cl. 34-7) This invention relates to a phase of the production of gypsum wallboard and comprises a division of my prior application Serial No. 567,162, filed February 23, 1956, now US. Patent No. 2,909,850, issued on October 27, 1959.

Although the production of gypsum wallboard is quite well standardized, a brief description of the general process of production is as follows:

Calcined gypsum, together with other ingredients, is admixed by suitable devices to form a rather thick slurry which is discharged onto a continuous paper-back cover sheet which is carried forward on an endless conveyor, generally termed a forming belt. Devices along the edge of the forming belt turn the back cover sheet edge upwardly and inwardly to contain the slurry which has been deposited. A face cover sheet is then applied, and the sandwich so formed then passes under leveling rolls or the like which equalize and determine the thickness of the board. As the board proceeds the gypsum mix sets and the wet sheet is cut to suitable lengths. Such formed lengths of wet board are then fed into a drier where they are dried to issue at the far end of the drier as finished wallboard.

The drier has also become quite conventionalized and ordinarily comprises a suitable elongated housing in which there are generally eight levels or decks to which the wet sheets are fed by a suitable feeder devise. Each of these drying decks in the drier comprise roller conveyors, some of which are positively driven, as by sprockets and chains, so that the boards which have been fed into the drier are carried through on the eight levels and finally discharged at the far end of the drier.

The drying is accomplished by circulating heated air, or possibly more specifically by super-heated steam at atmospheric pressure, and generally the over-all drier is made up of a plurality of identical drying circuits so that the temperature of drying and temperature gradient in each section may be more closely controlled. Each such section of the drier comprises an exhaust header feeding into the intake of large centrifugal fans which then discharge through a common duct over heaters which re-heat the circulating medium to then return into the drier through inlet headers provided at the other end. In a drier thus comprised of a plurality of units, as referred to, it is, of course, to be understood that the roller conveyors for carrying the board through the length of the drier are continuous, as is the main drier housing.

In drying the gypsum wallboard, the sections of the drier are zoned in decreasing temperature steps; the board incorporating its highest Water content as it goes into the drier, cold as compared with the temperature in the drier, is in such initial or first section subjected to high temperature and as the board is heated and its water content is driven off, the temperature to which it is subjected for drying is somewhat decreased in each of the succeeding drier sections. Since, for the most economic production, the highest possible rate of drying of the board is that which is employed, such situation creates a serious diificulty. When the gypsum board dries, that which is termed excess water or unbound water is driven off, but there still remains two molecules of water attached to each molecule of calcium sulfate, the basic mineral,

3,088,218 Patented May 7, 1963 ice which in its hydrated form we know as gypsum. If dry board is further heated in the vicinity of the boiling point of water, that is, to around 212 F., one and one-half of the two molecules of bound or attached water will be boiled off and the gypsum will then be calcined gypsum as, for example, a loose, powdery material such as might be bought at the hardware store as plaster of Paris. The bound or attached water of crystallization may also be driven off at lower temperature as there is both a time and temperature relationship involved.

Such dehydration of the set gypsum core of gypsum board is, of course, undesirable since its effect is to destroy the board. It is common that in drying gypsum board in a drier such as is described the board does not pass through the final section of the drier at a high enough speed, or the temperature is maintained too high, or due to a combination of such conditions the board is subjected to excessive dehydration and the material of the core is more or less calcined and harmed.

The principal object of this invention is to incorporate in a drier construction certain modifications which have the effect of protecting the edge portions of the gypsum board being dried from being over-dried and calcined. It will be understood, of course, that the side edges of the gypsum boards being dried are most susceptible to injury by over-drying and calcining, since at the edges of the board evaporation can progress rapidly in three directions, that is, the moisture may be evaporated through the top surface of the board, through the edge surface, and through the bottom surface. By the provision of the constructionwhich will be hereinafter fully described, the edge portions of the board being dried are protected from the rapid circulation of the hot drying medium and thus it is possible to maintain temperatures higher than normal in the drying of the gypsum board, and also, at the same time, protect the edges of the board from overdrying with consequent calcination. From the foregoing it is obvious that it is also an objective of the invention hereof to enable a higher production rate to be obtained through modification of the drier structure, and to thereby enable the production of more and better board from a given production line.

Other and further objects of the invention will be apparent on reading the following specification taken in conjunction with the accompanying drawings illustrative of the inventions hereof.

FIG. 1 is a perspective view of a drier unit;

FIG. 2 is a cross section taken on line 22 of FIG. 1;

FIG. 3 is a cross section taken on line 3-3 of FIG. 1;

FIG. 4 is a somewhat enlarged detail showing the mounting of the deflector elements; and

FIG. 5 is a section taken substantially on line 5-5 of FIG. 4.

Referring to the illustrations of the drawings, the drier unit illustrated in FIG. 1 is more or less conventional, but it is to be understood that such is merely for the purpose of describing the general structure of a drier for the drying of gypsum wallboard, and that such is illustrative only. Actually, such serves as an illustration of the functions of a drier in that it discloses an inclosing housing through which the gypsum board to be dried may be suitably conveyed and in connection with which heated air is moved relative the surfaces of the board being dried in order that the excess moisture may be removed from the material.

The general construction of a drier of this type includes a housing, an elongated inclosure, which is shown as comprising the upright beam members 10, and closure panels 11 connect forming spaced vertical walls primarily defining the drying chamber. Across the top of these walls and constituting the structure, a tunnel-like apparatus, there is provided a roof or top portion which comprises largely the bottom or lower side of air duct 12 with filler members 13 applied in case duct 12 is not of suflicient width to span the full width between the sidewalls. At each end of this tunnel-like apparatus there is indicated, as at 14 and 15, charging and discharging devices, respectively, for feeding the board to be dried into and out of the drier. It is to be understood, of course, that the entire drier structure for drying gypsum wallboard will normally comprise three such apparatus connected serially to constitute the drier, and that in such case suitable feeding device 14- is provided at the entrance end of the drier with a suitable discharge device supplied at the discharge end of the device.

Each of such drier sections is provided with an aircirculatingsystem which includes suitable ducts, blowers and heater devices for circulating and heating the drying medium. As illustrated at what has been referred to as the discharge end of a drier unit, there are provided suitable collecting header ?16 through whichthe drying medium is drawn by blowers 17 to which such headers 16 are connected. The blowers 17 may be driven by any suitable drive mechanism indicated as by motors 18. The blowers 17 discharge into the main duct :12, previously referred to, which extends lengthwise of the drier unit and conveys the air to the forward or entrance end of the unit. Towards the entrance end of the drier unit in the enlarged portion of duct 12, that portion in which there are shown doors or ports '19, there are provided suitable heater elements over which the circulating drying medium passes to be heated for return at the entry end of the drier. At its forward end, at the entrance end of the drier unit, duct 12 discharges into a cross header 25 which discharges through inlet headers 26 into the forward or entrance end of the drier unit.

In accordance with the foregoing description, it should be readily evident that the drier comprises a tunnel-like inclosure through which the wet board, which is to be dried, passes and wherein the board is dried by the heated medium which is circulated through the duct work as described, discharged into the drier at its entrance end to pass lengthwise through the drier and over the boards being conveyed therethrough, and finally at the discharge end is pulled out of the drier by the blowers and recirculated. In such drier there is provided a discharge stack 27 through which a portion of the circulating medium is allowed to discharge to atmosphere. Ordinarily there is suflicient air leakage into the drier to provide such fresh or make-up air as is required to replace the moistureladen air which discharges through stack 27, but if such leakage is insuificient it is understood that suitable additional inlet ports may be provided whereby the desired limited amount of fresh make-up air may be introduced into the system. As previously referred to, the entire drier apparatus for drying gypsum wallboard usually com: prises three such units serially connected with continuous conveyors extending from end to end. In such drier, made up of three connected units as described, it will be readily understood that such may be zoned as to the temperature of the drying medium, and that ordinarily the circulating drying medium in the first or entrance section is that which is maintained highest, that the temperature in the next circulating system is maintained slightly lower,

and that finally, in the circulating system at the discharge end, a still lower temperature is maintained so that the boards will not be over-dried or calcined. Of course, the temperatures in the respective zones will be suitably controlled and adjusted, but since this phase of the operation is not essential to the invention hereof, and as it is well understood by those skilled in the art, such has not been specifically illustrated and will not be described.

As above referred to, the principal objective hereof is that of providing in the basic drier, as generally described, a construction which will provide for protection of the edges of the gypsum wallboards being dried. The function of such construction is that of, to an extent, isolating the edge portions of the boards from the effect of the high temperature of the circulating drying medium to prevent the edges from drying at a faster rate than does the remaining portion of the boards, and to thereby avoid calcination of the edge portions of the board cores.

Such isolation of the edge portions of the boards is not to be understood as a complete isolation. It is such only as to bring about an equalization of the drying of the edge portions of the boards as compared with the rate of drying of the remaining portions of the boards, and it is to be understood that the edge portions are to be dried and consequently the construction or means provided for the isolation of the edge portions of the boards must, nevertheless, provide only protective isolation.

As illustrated in the drawings, the drier is shown as having eight drying decks, so that eight strings of board are dried simultaneously. These drying decks are actually vertically spaced roller conveyors, each made up of horizontally spaced rolls, suflicient of which are driven rolls so as to provide for conveying the boards through the drier. The rolls are designated by the numeral 30', and it is to be understood, of course, that such are suitably supported at their ends in bearings or journals 31 which are mounted to the drier structure and in the drawings indicated as mounted to the interior upright beam members 32.

For providing the desired isolation of the edge portions of boards 33 being conveyed through the drier, there is provided a partition-like construction which, as shown, is positioned toward each end of the conveyor roll series but inwardly of the ends of the rolls. These partition-like structures are spaced at something less than the width of the boards being dried, and since normally gypsum wallboards are 4' widths, the spacing between these partitionlike structures would ordinarily be approximately between 3' and 4' with a 3'-6" spacing probably being the optimum. It is to be understood, of course, that the operating characteristics of a-drier of the character involved will vary somewhat, and that in various installations the optimum spacing between the protective partition-like constructions will vary somewhat within the limits as stated, depending upon the operating characteristics of the particular drier and also somewhat dependent on the drying characteristics of the board being produced. The best spacing must be determined for any specific condition, but this is merely a detail of operation and in no way affects the constructions involved.

The protective partion which is mounted spaced somewhat inwardly from the ends of the rolls for the purpose of protecting the board edges from calcination while being dried, comprises construction which will now be described.

Each partition comprises an elongated sheet of material which may comprise a suitably fabricated, heavy weight galvanized sheet iron or other relatively rigid sheet material which can be expected to stand up under the conditions existing in the drier. Such substantially rigid portion of the partition is identified by numeral 35. Such member 35 is mounted to the drier frame by means of suitable angle irons such as 36 and 37, or equal structure. Angle iron 36 is shown as riveted to member 35, whereas angle iron 37 is shown as bolted to interior beams 32. Instead of securing angle iron 36 to member 35 by rivets 38 it will, of course, be understood that any other suitable manner of securing, as for example welding, may be utilized. The two angle irons 36 and 37 overlap, as shown, and they may be secured as by bolt 39. Preferably the bolt holes for receiving bolt 39 are elongated so that by loosening bolt 39 the partition member 35 may be moved toward or away from the wall of the drier. Likewise with respect to bolt 40, securing angle iron 37 to beam 32, preferably the bolt hole in the angle iron and through which bolt 40 passes is elongated so that a degree of vertical adjustment may be had.

Member 35, as described, is mounted between each deck or roller conveyor of the drier. This partition member 35 does not constitute a complete closure extending from a board 33 on one deck to a board 33 on an adjacent deck. For completing an individual partition member, somewhat flexible or resilient strip material, as 45, is mounted at the top and bottom of member 35. These strips 45 must be of more or less flexible or resilient material which will stand up under the conditions existing in the drier, and for this purpose there is suggested a glass fiber fabric which may be woven or non-woven but suitably bonded, or may comprise suitable heat-resistant synthetic rubber or silicone resin material, or the like.

Since these strips 45 are for the purpose of substantially partitioning the space between adjacent gypsum board sheets passing through the drier, the necessity that they be of somewhat flexible or resilient material should be apparent. If these strips 45 were rigid material it would be necessary that their outer edges be appreciably spaced from the respective bottom and top surfaces of adjacent sheets in order that there would be no danger of the rigid material marring the paper cover sheets of the boards. Of course, if desired, the rigid sheet form partition members 35 could extend substantially the full height of the space between adjacent sheets of board supported on the conveyors, but in such case it would, of course, be necessary, to avoid the possibility of marring, that the edges of such partition member be an appreciable distancefrom the board surfaces to assure that such would not be damaged.

The flexible strip members 45 which are mounted to partition member 35 are shown as mounted in what might be termed a ball and socket joint, that is, the top and bottom edges of the member 35 are flared to substantially tubular form, as at 46, but which is slotted in order that bead 47 formed on an edge of strip material 45 may be slid into and secured in such tubular portion 46.

It will be understood, of course, that considering any specific partition member 35 that such along its bottom edge is provided with a straight edge, whereas along its top edge it will be suitably recessed or cut out to receive the lower portions of the conveyor rolls, this feature of the construction being clearly apparent in FIG. 5 of the drawings. The strip member 45, which is mounted to the lower end of partition member 35, is merely a straight strip, which, however, will preferably be in sections which may conveniently be entered into and removed from the lower tubular member 46. For the purpose of inserting or removing such lower flexible strip members 45, slots or openings 48 are provided in a side Wall of lower tubular member 46. It will be understood that a suitable length of plain lower strip member 45 may be entered into such slot 48 and head 47 on the strip may then be slid into the tubular member 46. The upper flexible strip member 45 is, of course, in sections such as to extend between adjacent rollers, horizontally spaced in a coveyor deck, since the upper flexible members extend up between the rollers to adjacent the under side of the board carried on such roller. Preferably, at each end such sections of the upper strip member are suitably shaped, as at 49, to substantially embrace the roll surfaces. It is, of course, understood that in all instances it is preferable that the flexible strip members be at their edges spaced by a slight amount from the boards being conveyed and from the adjacent rollers between which the upper strips are positioned.

It will be seen, in accordance with the just above described construction, by providing such constructions, that along the side edges of the drier a portion is partitioned off so that the hot drying blast traveling through the drier is substantially restricted to that portion of the drier between such partitions and is substantially prevented from entering the partitioned ofl portions along the edges of the drier, whereby the board edges are subjected to less drastic drying than is the remainder of the board.

Since for every drier and for each diflerent type of board being dried the conditions of drying will'vary somewhat, it is to be understood that it is not desired that the partitioned edge portions be completely isolated from the center portion of the drier where the drying medium is freely circulated. It is necessary that the edge portions of the boards 33 be dried, and therefore it is the function of the partitions to cut down the circulation of the hot drying medium in the partitioned off edge portions of the drier and not to completely prevent access of hot drying medium thereto. In some cases, depending upon the particular characteristics of the drier, and the drying characteristics of the particular gypsum wallboard involved, it may be necessary to level out some of the upper fabric members 45 of the partition construction and suitably space the ends of the bottom fabric elements 45. In any case, of course, since the edges of the upper and lower fabric members 45 should be kept out of actual contact with the boards and the periphery of rollers 30, there will be some leakage of hot drying medium into the partitioned off edge portions.

Alternatively, or in conjunction with the described partition construction, evaporation from the edges of boards 33 may be retarded so that they do not dry faster than do the central portions of the boards by utilizing fluid sprays, which are so adjusted as to maintain a lower rate of evaporation of moisture from the edge portions of the boards 33. Such can be accomplished by positioning spray heads within the drier at approximately board level for each deck, and then suitably spaced along the length of the drier. In the drawings there has been indicated a main fluid header 50 from which longitudinal pipes 51 extend along the length of the drier approximately at the level of the boards on each of the conveyor decks. In the drawings, in order not to obscure other features, only one of these longitudinal pipes 51 has been shown extending the full length of the drier; the others are merely illustrated as short, broken-01f sections. From each of these fluid distributor pipes 51 there is indicated a connecting pipe 52 extending in and through the side of the drier and positioned approximately mid-way between each pair of exterior beams 10. These distributor pipes 52 extend just inside the drier side panels 11 and are provided with wide angle spray heads 53, preferably designed to discharge substantially or at only a very small angle relatively perpendicular to the axis of distributor pipes 52.

'In case such spray heads 53, as just described, are provided, the partition structures heretofore referred to and described are omitted, and a cooling fluid, for example, water, is supplied to and discharged from the spray heads 53, which should be of the nebulizing or misting type so that the cooling fluid is substantially discharged as a fog of extremely small particles or substantially atomized.

Alternative to supplying cooling water to the spray heads 53, there may be supplied air at relatively low pressure, in which case, of course, it is understood that nozzles of suitable design would be substituted for water- -atomizing nozzles. Such air-discharge nozzles similarly, however, should discharge the air substantially laterally with respect to the supply-distributing pipes 52.

In either case, whether the nozzles 53 are provided for discharging Water or air, their function is that of blanketing the edge portions of the boards 33 as they are passing through the drier, and to consequently protect such edges from the full effect of the heated drying medium circulating through the drier. "In the case water is fogged or atomized into the drier adjacent the sides thereof, such, of course, not being heated, will absorb some of the heat along the edge portions of the drier and it will form a fluid partition or fluid face which will substantially prevent the hot circulating drying medium from circulating over and around the edge portions of the boards being dried. When air is supplied by the nozzles, such has substantially the same effect as does the fogging by the fluid atomizing nozzles except that the air supply has less heat-absorbing capacity .than does the'water fog, but otherwise the action in protecting the edges of the board is substantially similar.

It is, of course, readily apparent that it may be necessary or desirable that both constructions or methods described for cooling the edge portions of board being dried, or, possibly, more properly stated for preventing overheating and recalcination of the edges of board being dried, may be employed at the same time. That is to say, edge cooling or prevention of overheating of the edges may be accomplished either through establishing a relatively static zone along the board edges, or by so restricting the flow of drying medium that the edges of the board are not subjected to the elfect thereof to the extent that the portion of the board inwardly from the edges thereof are affected. If conditions such as leakage of drying medium past the partitions is over-drying the board edges, then at least some of the spray heads may be activated to obtain the desired rate of drying of the edges of the board. On the other hand; if the edge drying is excessive when the sprays alone are in use, the partitions may be availed of to supplement the retardation of the drying of the edges of the board through restriction of the flow of drying medium. In either case, as just above referred to, it might be said that the two systems are utilized in conjunction of necessity, but it should be understood that it might be desirable to design the over-all apparatus such that at all times both systems for preventing over-drying and recalcinating of the edges of the board cooperate to obtain the desired result.

It is deemed that in the foregoing there has been fully disclosed the apparatus serving for the protection of the edges of gypsum boards while being dried in a conventional drier, whereby the edges are protected against calcining. The specific apparatus as disclosed is, of course, susceptible to various design modifications, and it is to be understood that the specific disclosures of the drawings and specification are to be taken merely as illustrative of the inventions and as disclosing that form of the inventions now considered to constitute the preferred form.

The inventions thereof having been fully disclosed, I claim:

1. The method in the drying of gypsum wallboard containing water in excess to that required for rehydration and comprising the steps, while conveying the board through a tunnel-form drier and while subjecting the major surfaces to the drying effect of flowing drying medium, of providing adjacent to and around the side edge portions only of the board a relatively static gaseous cushion incorporating a content of substantially atomized cooling fluid.

2. In a tunnel-form drier, for drying gypsum wallboard and including therein side walls, a plurality of spaced superimposed roller conveyors and means circu lating drying medium longitudinally through the drier, the improvement comprising partition means positioned between contiguous pairs of conveyors, means mounting and supporting the partition means adjacent and inwardly of the ends of the rollers of the conveyors, thepartitions extending from substantially just slightly below the level of the top of the rolls of the upper conveyor of a contiguous pair ofconveyors to short, by a distance slightly in excess of the thickness of the boards being dried, of the level of the top of the rolls of the lower conveyor of the pair thereof to form a central chamber and a pair of chambers flanking said central chamber extending longitudinally of said drier and widthwise confining the circulating drying medium substantially entirely to said central chamber and means supplying secondary cooling medium to the space defined by said flanking chambers.

3. In a tunnel-form drier for drying gypsum wallboard and including therein side walls, a plurality of spaced superimposed conveyors and means circulating drying medium longitudinally through the drier, the improvement comprising partition means the lower edges of which are spaced from the conveyor contiguous thereto a distance not less than the thickness of the gypsum wallboards being dried, means mounting and supporting the partition means between contiguous pairs of conveyors adjacent and inwardly of the side edges thereof to form a central chamber and a pair of chambers flanking said central chamber extending longitudinally of said drier and widthwise confining the circulating drying medium substantially entirely to said central chamber, fluid discharging nozzles positioned within said flanking chambers, means mounting and supporting the fluid discharging nozzles, and' means connected to said nozzles for providing said fluid thereto.

4. In a tunnel-form drier for drying gypsum wallboard and including therein side' walls, a plurality of spaced superimposed conveyors and means circulating drying medium longitudinally through the drier, the improvement comprising partition means the lower edge of which is spaced from the conveyor'contiguous thereto a distance not less than the thickness of a gypsum wallboard being dried, means mounting and supporting the partition means between contiguous pairs of conveyors adjacent and inwardly of the side edges thereof to form a central chamber and a pair of chambers flanking said central chamber extending longitudinally of said drier and widthwise confining the circulating drying medium substantially entirely to said central chamber, fluid discharging nozzles mounted in said flanking chambers discharging cooling fluid principally in the direction parallel to the drier side Walls, means mounting the fluid discharging nozzles for discharge between the contiguous faces of the drier side walls and the partition means, and means connected to said nozzles for supplying said fluid thereto. 5

References Cited in'the file'of this patent UNITED STATES PATENTS 

1. THE METHOD IN THE DRYING OF GYPSUM WALLBOARD CONTAINING WATER IN EXCESS TO THAT REQUIRED FOR REHYDRATION AND COMPRISING THE STEPS, WHILE CONBEYING THE BOARD THROUGH A TUNNEL-FORM DRIER AND WHILE SUBJECTING THE MAJOR SURFACES TO THE DRYING EFFECT OF FLOWING DRYING MEDIUM, OF PRODIVING ADJACENT TO AND AROUND THE SIDE EDGE PORTIONS ONLY OF THE BOARD A RELATIVELY STATIC GASEOUS CUSHION INCORPORATING A CONTENT OF SUBSTANTIALLY ATOMIZED COOLING FLUID. 